Biological information detector, biological information measuring device, and method for designing reflecting part in biological information detector

ABSTRACT

A biological information detector includes a wristband, a housing, an opening, a light-emitting part, a reflecting part, a light-receiving part, and a protecting part. The opening is defined in a surface of the housing adapted to face a surface of the wrist of the user. The light-emitting part is disposed inside the housing and configured to emit green light. The reflecting part is disposed in periphery of the light emitting part, and configured to reflect the light emitted by the light-emitting part, wherein the reflecting part is disposed inside the housing. The light-receiving part is disposed inside the housing, and configured to receive reflected light reflected at a detection site of the wrist of the user. The protecting part is configured to protect the light-emitting part and the reflecting part, and is disposed at the opening of the housing to contact with the detection site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 14/520,896 filed on Oct. 22, 2014, which is a continuationapplication of U.S. application Ser. No. 14/304,106 filed on Jun. 13,2014, which is a continuation application of U.S. application Ser. No.13/015,210 filed on Jan. 27, 2011, now U.S. Pat. No. 8,823,944. Thisapplication claims priority to Japanese Application No. 2010-0022836filed on Feb. 4, 2010. The entire disclosures of U.S. application Ser.Nos. 14/520,896, 14/304,106 and 13/015,210 and Japanese Application No.2010-0022836 are hereby incorporated herein by reference.

BACKGROUND

Technological Field

The present invention relates to a biological information detector, abiological information measuring device, and method for designing areflecting part in the biological information detector and the like.

Background Technology

A biological information measuring device measures human biologicalinformation such as, for example, pulse rate, blood oxygen saturationlevel, body temperature, or heart rate, and an example of a biologicalinformation measuring device is a pulse rate monitor for measuring thepulse rate. Also, a biological information measuring device such as apulse rate monitor may be installed in a clock, a mobile phone, a pager,a PC, or another electrical device, or may be combined with theelectrical device. The biological information measuring device has abiological information detector for detecting biological information,and the biological information detector includes a light-emitting partfor emitting light towards a detection site (e.g., finger or arm) of atest subject (e.g., a user), and a light-receiving part for receivinglight having biological information from the detection site.

There is disclosed in Japanese Laid-Open Publication No. 2004-337605 areflection-type light sensor in which a light-emitting element and alight-receiving element are coaxially provided. The reflection-typelight sensor described in Japanese Laid-Open Publication No. 2004-337605is designed so that the detection sensitivity of the light-receivingelement is at a maximum when a detection target (e.g., a finger) ispositioned at a predetermined distance away from a window fortransmitting light emitted from the light-emitting element. In paragraph[0032] in Japanese Laid-Open Publication No. 2004-337605, it isdisclosed that the emission angle of the light-emitting element can bechanged, the size of a substrate can be changed, and the curvature orfocal point of a reflecting surface can be changed, in order to set apeak position at which the detection accuracy is at a maximum.

Light emitted by the light-emitting element illuminates a detection siteof a test subject via a light-transmitting member (corresponding to awindow part in Japanese Laid-Open Publication No. 2004-337605). A partof the light emitted by the light-emitting element is reflected on asurface (and a vicinity of the surface) of the light-transmittingmember. The reflected light is light that has been reflected directly onthe surface (and a vicinity of the surface) of the light-transmittingmember (i.e., directly reflected light), and directly reflected light isinvalid light that does not have biological information (i.e., noiselight). In an instance in which the directly reflected light (i.e.,invalid light) is incident on a light-receiving region of thelight-receiving element, the S/N (i.e., signal-to-noise ratio) of abiological information detection signal outputted from thelight-receiving element decreases. In order to improve the measurementsensitivity of a biological information measuring device, it isimportant to design a light-collecting optical system (i.e., areflecting part) so as to minimize incidence of directly reflected light(i.e., invalid light) on the light-receiving region of thelight-receiving element. Merely adjusting the focal length of thereflecting surface as with Patent Citation 1, for example, does notremove the effect of reflected light that has been reflected on asurface side of the light-transmitting member (i.e., the window part),i.e., the effect of directly reflected light (e.g., a decrease in theS/N of the detection signal outputted from the light-receiving element).

SUMMARY

A biological information detector according to one aspect includes awristband, a housing, an opening, a light-emitting part, a reflectingpart, a light-receiving part, and a protecting part. The wristband isadapted to be attached to a wrist of a user. The housing is connected tothe wristband and adapted to be placed on the wrist of the user. Theopening is defined in a surface of the housing adapted to face a surfaceof the wrist of the user. The light-emitting part is disposed inside thehousing and configured to emit green light. The reflecting part isdisposed in periphery of the light emitting part, and configured toreflect the light emitted by the light-emitting part, wherein thereflecting part being disposed inside the housing. The light-receivingpart is disposed inside the housing, and configured to receive reflectedlight reflected at a detection site of the wrist of the user. Theprotecting part is configured to protect the light-emitting part and thereflecting part, and is disposed at the opening of the housing tocontact with the detection site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a drawing used to represent an example of a configuration ofa biological information detector and a preferable design for areflecting part;

FIG. 1B is the drawing used to represent an example of the configurationof the biological information detector and a preferable design for thereflecting part;

FIG. 2 is a drawing representing a specific example of a configurationof the biological information detector;

FIG. 3 is a drawing representing, with respect to the plan view, anouter appearance of a substrate coated with a light-transmitting film;

FIG. 4A is a drawing representing an example of intensitycharacteristics of light emitted by a light-emitting part and an exampleof sensitivity characteristics of a light-receiving part;

FIG. 4B is a drawing representing an example of the intensitycharacteristics of light emitted by the light-emitting part and anexample of the sensitivity characteristics of the light-receiving part;

FIG. 5 is a drawing representing an example of light transmissioncharacteristics of the substrate having the light-transmitting film;

FIG. 6A is a drawing representing parameters relating to designing thereflecting part having the reflecting surface that uses a part of aspherical surface, and to an example of a method for designing thereflecting part;

FIG. 6B is a drawing representing parameters relating to designing thereflecting part having the reflecting surface that uses the part of thespherical surface, and to an example of the method for designing thereflecting part;

FIG. 7 is a drawing representing an example of dimensions of mainconfigurations in the biological information detector;

FIG. 8A is a drawing used to describe a behavior of directly reflectedlight in an instance in which df=1.18 mm (Δh=0.4 m);

FIG. 8B is a drawing used to describe the behavior of directly reflectedlight in the instance in which df=1.18 mm (Δh=0.4 m);

FIG. 9 is a drawing used to describe a behavior of directly reflectedlight in an instance in which df=1.278 mm (Δh=1.3 m);

FIG. 10 is a drawing used to describe a behavior of directly reflectedlight in an instance in which df=1.556 mm (Δh=2.2 m);

FIG. 11 is a drawing representing a change in a ratio (%) of the amountof directly reflected light incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 12 is a drawing representing a change in a ratio (S/N) of validlight having pulse rate information incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 13 is a drawing representing a change in the ratio (%) of theamount of directly reflected light incident on the light-receiving part(photodiode) in an instance in which Δh is gradually increased where theaperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 14 is a drawing representing a change in the ratio (S/N) of validlight having pulse rate information incident on the light-receiving part(photodiode) in an instance in which Δh is gradually increased where theaperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 15 is a drawing representing a change in the ratio (%) of theamount of directly reflected light incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=3.6 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 16 is a drawing representing a change in the ratio (%) of theamount of directly reflected light incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.3 mm, and δ=0.3 mm;

FIG. 17A is a drawing used to describe a reflecting surface including apart of a paraboloid (i.e., a paraboloid mirror);

FIG. 17B is a drawing used to describe the reflecting surface includingthe part of the paraboloid (i.e., a paraboloid mirror);

FIG. 18 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 0.7 mm where the aperture diameterφ=4.4 mm, thickness t of contact member 19-2=0.4 mm, and height(spacing) δ of spacer member 19-1=0.53 mm;

FIG. 19 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 1.0 mm where the aperture diameterφ=4.4 mm, thickness t of contact member 19-2=0.4 mm, and height(spacing) δ of spacer member 19-1=0.53 mm;

FIG. 20 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 1.3 mm where the aperture diameterφ=4.4 mm, thickness t of contact member 19-2=0.4 mm, and height(spacing) δ of spacer member 19-1=0.53 mm;

FIG. 21 is a drawing representing a change in the ratio (%) of theamount of directly reflected light incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm;

FIG. 22 is a drawing representing an external appearance of an exampleof a biological information measuring device (i.e., a wrist pulse ratemonitor) including the biological information detector; and

FIG. 23 is a drawing representing an example of an internalconfiguration of the biological information measuring device.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred Embodiments of the Invention

A description shall now be given for the present embodiment. The presentembodiment described below is not intended to unduly limit the scope ofthe claims of the present embodiment. Not every configuration describedin the present embodiment is necessarily an indispensible constituentfeature of the invention.

First Embodiment

First, a description will be given for an overview of a configuration ofthe biological information detector and the biological informationmeasuring device, examples of behavior of light emitted by thelight-emitting part, and other details.

Overview of Configuration of Biological Information Detector, and OtherDetails

FIGS. 1A and 1B are drawings used to describe an example of aconfiguration of a biological information detector and a preferabledesign for a reflecting part. FIG. 1A shows a state in which reflectedlight (i.e., valid light) is incident on a light-receiving region of alight-receiving part. FIG. 1B shows a state in which light reflected ona contact-surface side of a contact member forming a protecting part(i.e., directly reflected light; invalid light) is incident on thelight-receiving region of the light-receiving part. The structure of thebiological information detector 200 shown in FIGS. 1A and 1B isidentical, and parts that are the same in each drawing are affixed withthe same reference numerals.

A configuration of the biological information detector 200 will now bedescribed. The biological information detector 200 can be installed in,e.g., a pulse rate monitor that can be fitted onto a wrist of a personusing a wristband or another component (and is not limited to thedescription given above). Other than pulse rate information (i.e., heartrate information), the biological information may also be blood oxygensaturation, body temperature, or another variable.

As shown in FIGS. 1A and 1B, the biological information detector has: alight-emitting part 14 (with an LED or another light-emitting element)for emitting light R1 directed at a detection site 1 (e.g., finger, arm,or wrist) of a test subject 2 (e.g., a human body); a light-receivingpart 16 (with a photodiode or another light-receiving element) forreceiving light R1′ having biological information produced by the lightR1 emitted by the light-emitting part 14 being reflected at a bloodvessel BV, which is a biological information source at the detectionsite 1; a reflecting part 18 for reflecting light having biologicalinformation; a protecting part 19; and a light-transmitting substrate11.

The light-receiving part 16 has a light-receiving region (i.e.,light-receiving surface) 16-1 on a side towards the reflecting part 18.The reflecting part 18 has a reflecting surface (i.e., a reflectingmirror) that is a quadric surface. The reflecting surface can beprovided on an inner surface of a dome provided on a light path betweenthe light-emitting part 14 and the light-receiving part 16. For example,a main body of the reflecting part 18 is made of a resin, and the innersurface (i.e., a quadric surface formed on a side towards thelight-receiving part 16) of the main body is subjected to mirror surfacefinishing (e.g., a metal film or a similar structure is formed on thesurface), thereby making it possible to form the reflecting part (i.e.,a reflecting optical system).

The protecting part 19 has a contact member 19-2 provided with a contactsurface SA in contact with (or at least has a possibility of being incontact with) the test subject (i.e., measurement target, e.g., a humanbody), and a spacer member 19-1. The contact member 19-2 and the spacermember 19-1 is formed from a material that is transparent with respectto a wavelength of light R1 emitted by the light-emitting part 14 (e.g.,glass). Specifically, the contact member 19-2 is a light-transmittingmember. The protecting part 19 is also an accommodating part foraccommodating the light-emitting part 14 (i.e., an accommodatingcontainer or a protective case), and has a function of protecting thelight-emitting part 14.

The substrate 11 is arranged between the reflecting part 18 and theprotecting part 19. The substrate 11 has two main surfaces. In thepresent specification, a main surface of the substrate 11 on a sidetowards the light-emitting part 14 may be referred to as a first surface(or a reverse surface), and a main surface of the substrate 11 on a sidetowards the reflecting part 18 may be referred to as a second surface(or a front surface). The light-emitting part 14 is arranged on thefirst surface (i.e., the reverse surface) of the substrate 11, and thelight-receiving part 16 is arranged on the second surface (i.e., thefront surface). The light-emitting part 14 and the light-receiving part16 have an overlap with respect to the plan view. A surface of thelight-emitting part 14 that is in contact with the substrate 11 and asurface of the light-receiving part 16 that is in contact with thesubstrate 11 face each other so as to be separated by a distance equalto the thickness of the substrate 11. The substrate 11 is formed from amaterial that is transparent with respect to the wavelength of lightemitted by the light-emitting part 14 (e.g., polyimide or polyarylate).Specifically, the substrate 11 is a light-transmitting substrate.

Since the substrate 11 is arranged between the reflecting part 18 andthe protecting part 19, even in an instance in which the light-emittingpart 14 and the light-receiving part 16 are arranged on the substrate11, there is no need to separately provide a mechanism for supportingthe substrate 11 itself, and the number of components is smaller. Also,since the substrate 11 is formed from a material that is transparentwith respect to the emission wavelength, the substrate 11 can bedisposed on a light path from the light-emitting part 14 to thelight-receiving part 16. Therefore, there is no need to accommodate thesubstrate 11 at a position away from the light path, such as in aninterior of the reflecting part 18. A biological information detectorthat can be readily assembled can thus be provided. Also, the reflectingpart 18 makes it possible to increase the amount of light incident onthe light-receiving part 16, thereby increasing the detection accuracy(i.e., signal-to-noise ratio) of the biological information detector.The biological information source (e.g., the blood vessel BV) may benear the contact surface SA.

Example of Behavior of Light Emitted by the Light-Emitting Part

Next, a description will be given for an example of behavior ofreflected light having biological information, with reference to FIG.1A. The blood vessel BV, which is a biological information source, islocated, e.g., within an interior of the detection site 1 (e.g., afinger or an arm (or in a narrower sense, the wrist)) of the testsubject 2 (e.g., a human body). Light R1 emitted by the light-emittingpart 14 (specifically, a main light beam, i.e., an expression meaninglight that does not contain reflected light reflected on another member)travels into the interior of the detection site 1 and diffuses orscatters at the epidermis, the dermis, and the subcutaneous tissue. Thelight R1 subsequently reaches the blood vessel BV, which is thebiological information source, and is reflected at the blood vessel BV.A part of the light R1 is absorbed by the blood vessel BV. Due to aneffect of the pulse, the rate of absorption at the blood vessel BVvaries, and the amount of reflected light R1′ reflected at the bloodvessel BV therefore varies. Therefore, biological information (e.g.,pulse rate) is thus reflected in the reflected light R1′ reflected atthe blood vessel BV.

The reflected light R1′ reflected at the blood vessel BV diffuses orscatters at the epidermis, the dermis, and the subcutaneous tissue. Inthe example shown in FIG. 1A, the reflected light R1′ passes through thesubstrate 11, is reflected on the reflecting part 18, and is directlyincident on a light-receiving region (i.e., light-receiving surface)16-1 of the light-receiving part 16. The expression “is directlyincident on” is used to express the fact that the light is not routedvia, e.g., a complex reflection process, but via, e.g., a smallestpossible number of reflections (i.e., via a simple path). A biologicalinformation detection signal outputted by the light-receiving part 16includes a pulsating component corresponding to the pulse. Therefore,the pulse rate can be measured according to the detection signal.

Next, a description will be given for an example of behavior ofreflected light (i.e., invalid light) reflected on a side of the contactmember 19-2 forming the protecting part 19 towards the contact surfaceSA (i.e., at the contact surface SA and a vicinity of the contactsurface SA (including an interface between the contact surface and thedetection site, as well as the skin surface and an inner side of theskin)) with reference to FIG. 1B. In FIG. 1B, a main light beam R2emitted by the light-emitting part 14 reflects once at a point N1 on thecontact member 19-2 on a side towards the contact surface SA (e.g., at apoint on the contact surface SA). A reflected light R2′ which hasreflected once (i.e., a once-reflected light) passes through thesubstrate 11, reflects again at the reflecting part 18, and is incidenton the light-receiving region 16-1 of the light-receiving part 16.

A main light beam R3 emitted by the light-emitting part 14 reflectstwice at positions N2 and N3 on the contact member 19-2 on a sidetowards the contact surface SA (e.g., at points on the contact surfaceSA). A reflected light R3′ which has reflected twice (i.e., atwice-reflected light) passes through the substrate 11, reflects againat the reflecting part 18, and is incident on the light-receiving region16-1 of the light-receiving part 16.

The reflected light R2′ and the reflected light R3′ are reflected lightsproduced by the light emitted by the light-emitting part 14 directlyreflecting on the surface (or a vicinity thereof) of the contact member19-2, which is a light-transmitting member (i.e., directly reflectedlight). The directly reflected light is an invalid light (i.e., noiselight) that does not have biological information. When the invalid lightthat does not have biological information is incident on thelight-receiving region 16-1 of the light-receiving part 16, the S/N(i.e., signal-to-noise ratio) of the biological information detectionsignal outputted from the light-receiving part 16 decreases. In order toimprove the detection accuracy of the biological information detector(i.e., to improve the measurement accuracy of the biological informationmeasuring device), it is important to design the reflecting part 18,which is a light-collecting optical system, so that directly reflectedlight (i.e., invalid light) can be inhibited from being incident on thelight-receiving region 16-1 of the light-receiving part 16.

Specific Example of a Configuration of the Biological InformationDetector, and Example of a Configuration of the Biological InformationMeasuring Device

FIG. 2 is a drawing representing a specific example of a configurationof the biological information detector. The upper side of FIG. 2 showsan example of a cross-section structure of the biological informationdetector, and the lower side shows positional relationships between eachpart with respect to the plan view. Parts in FIG. 2 that are the same asthose in FIGS. 1A and 1B are affixed with the same reference numerals(this also applies to other drawings described further below).

As shown in FIG. 2, the aperture diameter of the reflecting part 18 iscp. A reflecting surface 18-1 of the reflecting part 18 includes a partof a quadric surface (a spherical surface in this instance; thereflecting surface 18-1 may be, e.g., a substantially hemisphericalsurface). A bottom part of the hemispherical surface is open, notaccounting for the substrate or other components. The shape of theopening with respect to the plan view (i.e., the outer circumferentialshape of the reflecting surface with respect to the plan view) iscircular as shown in the lower side of FIG. 2, and the diameter (i.e.,the aperture diameter) is cp.

The height of the spacer member 19-1 in the protecting part 19 (may beregarded as a spacing between the substrate 11 and a surface of thecontact member 19-2 that is opposite the contact surface SA) is δ, andthe thickness of the contact member 19-2 is t.

As shown in the lower side of FIG. 2, the light-emitting part 14 and thelight-receiving part 16 have an overlap with respect to the plan view.The circumferential shape of each of the light-emitting part 14, thelight-receiving part 16, and the reflecting part 18 is a circle, each ofwhich circles being concentric with one another (with the center beingrepresented by s).

The substrate 11 is an optical component as a light-transmitting member,and is also a circuit substrate for forming a circuit. The substrate 11is, e.g., a printed circuit board. As shown in the upper side of FIG. 2,a wiring 62-1 for the light-receiving part 16 is formed on the firstsurface (i.e., front surface) of the substrate 11, and wiring 62-2, 62-3for the light-emitting part 14 are formed on the second surface (i.e.,reverse surface) of the substrate 11. The wiring 62-1 and thelight-receiving part 16 are connected by a bonding wire 63. The wiring62-2 and the light-emitting part 14 are connected by a bonding wire 62.The wiring 62-3 and the light-emitting part 14 are connected by abonding wire 65.

In a printed circuit board, the first surface (i.e., reverse surface)and the second surface (i.e., front surface) are preferably roughened toa certain extent to prevent printed wiring from detaching. However, whenthe first surface and the second surface of the substrate 11 areroughed, a problem is presented in that scattering of light increases.Therefore, in the example shown in FIG. 2, a light-transmitting film11-1 and a light-transmitting film 11-2 are respectively formed on thefirst surface (i.e., reverse surface) and the second surface (i.e.,front surface) in a light-transmitting region (or a region excluding alight-blocking region on which wiring or other components are formed) ofthe substrate 11. The light-transmitting films 11-1 and 11-2 are, e.g.,a light-transmitting resist film. Forming the light-transmitting films11-1 and 11-2 in the light-transmitting region of the substrate 11smoothens the roughness on each of the reverse surface and the frontsurface and reduces a difference in refractive index between thesubstrate 11 and air. Light is thereby inhibited from scattering at thefront surface and the reverse surface of the substrate 11 (in a broadersense, including the 11-1 and the 11-2). Also, since the difference inthe refraction index between the substrate 11 and air is smaller, thedegree to which light refracts in the substrate 11 can be reduced. Forexample, if the substrate 11 is set to a small thickness, light can beconsidered to travel straight through the substrate 11 without anysignificant refraction. This contributes towards making it possible toreadily simulate the behavior of light, and to readily design an opticalsystem in the biological information detector 200.

In the example shown in FIG. 2, a reflector 20 is provided. In aninstance in which the reflector 20 is referred to as a first reflectingpart, the reflecting part 18 having the reflecting surface 18-1including the quadric surface can be referred to as a second reflectingpart.

The reflector 20 has an effect of minimizing a spread of light emittedfrom the light-emitting part 14, increasing the directivity of light,and reducing the amount of invalid light emitted in a direction otherthan towards the detection site 1. The light-emitting part 14 has afirst light-emitting surface 14A and a second light-emitting surface(i.e., a side surface) 14B, and light is also emitted from the secondlight-emitting surface 14B. A protruding part (having, on an inner wallsurface of which, a reflecting surface that is an inclined or a curvedsurface) provided on a periphery of the reflector 20 has an effect ofreflecting light emitted from a side surface (i.e., the secondlight-emitting surface 14B) of the light-emitting part 14 (producing areflected light R4) and directing the light R4 towards the detectionsite 1.

The reflector 20 has a certain amount of width. Therefore, the reflector20 also has an effect of preventing a part of the directly reflectedlight (i.e., invalid light) reflected on a vicinity of the contactsurface SA of the contact member 19-2 of the protecting part 19 fromentering a side towards the reflecting part 18. For example, directlyreflected light incident from diagonally below is reflected on an endpart and other parts of the reflector 20, and the directly reflectedlight is thereby prevented from entering the side towards the reflectingpart 18. The reflector 20 also has an effect of reflecting a part of thedirectly reflected light towards the detection site 1, therebyconverting invalid light into valid light.

The effect of improving the S/N due to the preferable reflectivecharacteristics of the reflecting optical system that are realized bythe invention is thus supplemented with the effect of improving the S/Ndue to the reflector 20, and the detection accuracy of the informationdetector 200 is thereby further improved.

FIG. 3 is a drawing representing, with respect to the plan view, anouter appearance of the substrate coated with the light-transmittingfilm. FIG. 3 shows an outer appearance of the first surface (i.e., thefront surface; the surface on the side towards the light-receiving part16) of the substrate 11 with respect to the plan view. Thelight-transmitting film 11-1 is formed on a light-transmitting region(i.e., a region other than a light-blocking region) on the first surfaceof the substrate 11. The light-transmitting film 11-2 is formed on alight-transmitting region (i.e., a region other than a light-blockingregion) is formed on the second surface (i.e., the surface on the sidetowards the light-emitting part 14).

FIGS. 4A and 4B are drawings representing an example of intensitycharacteristics of light emitted by the light-emitting part and anexample of sensitivity characteristics of the light-receiving part. Inthe example of emission intensity characteristics shown in FIG. 4A, theintensity is at a maximum for light having a wavelength of 520 nm, andthe intensity of light having other wavelengths is normalized withrespect thereto. Also, the wavelengths of light emitted by thelight-emitting part 14 are within a range of 470 nm to 600 nm. Thelight-emitting part 14 includes, e.g., an LED. The light emitted by theLED has a maximum intensity (or in a broader sense, a peak intensity)within a wavelength range of, e.g., 425 nm to 625 nm, and light emittedby the light-emitting part 14 is, e.g., green in color.

FIG. 4B shows an example of sensitivity characteristics of thelight-receiving part. A gallium arsenide phosphide photodiode or asilicon photodiode are examples of the light-receiving part 16 that canbe used. However, the gallium arsenide phosphide photodiode has amaximum sensitivity (or in a broader sense, a peak sensitivity) forreceived light having a wavelength within a range of, e.g., 550 nm to650 nm. Since biological substances (water or hemoglobin) readily allowtransmission of infrared light within a wavelength range of 700 nm to1100 nm, the light-receiving part 16 formed by the gallium arsenidephosphide photodiode is more capable of reducing noise componentsarising from external light than the light-receiving part 16 formed bythe silicon photodiode.

Sensitivity characteristics shown in FIG. 4B are those for an instancein which a gallium arsenide phosphide photodiode is used as thelight-receiving part 16. In the example shown in FIG. 4B, thesensitivity is at a maximum for light having a wavelength of 565 nm, andthe sensitivity for light having other wavelengths is normalized withrespect thereto. The wavelength of light received by the light-receivingpart 16 at which the sensitivity is at the maximum is within the rangeof wavelengths emitted by the light-emitting part 14 shown in FIG. 4A,but is not within a range of 700 nm to 1100 nm, which is known as thebiological window (i.e., a wavelength region within which biologicalsubstances readily transmit light). In the example shown in FIG. 4B, thesensitivity of infrared light falling within the range of 700 nm to 1100nm is set at a relative sensitivity of 0.3 (i.e., 30%) or less. Thewavelength of light received by the light-receiving part 16 at which thewavelength is at the maximum (e.g. 565 nm) is preferably closer to thewavelength at which the intensity of light emitted by the light-emittingpart 14 is at the maximum (i.e., 520 nm) than a lower limit of thebiological window (i.e., 700 nm).

FIG. 5 is a drawing representing an example of light transmissioncharacteristics of the substrate coated with the light-transmittingfilm. Light transmission characteristics shown in FIG. 5 were obtainedby calculating the transmittance using intensity of light before passingthrough the substrate 11 and intensity of light after passing throughthe substrate 11.

In the example shown in FIG. 5, in a range of wavelength equal to orless than 700 nm, which is the lower limit of the optical window inbiological tissue, the transmittance is at a maximum for light having awavelength of 525 nm. Also, in the range of wavelength equal to or lessthan 700 nm, which is the lower limit of the opticalwindow in biologicaltissue, the wavelength of maximum transmittance of light passing throughat least one of the light transmission film 11-1 and thelight-transmitting film 11-2 falls within a range of ±10% of thewavelength of the maximum intensity of light generated by thelight-emitting part 14 shown, e.g., in FIG. 4A. It is preferable for thelight transmission film 11-1 (11-2) to selectively transmit lightemitted by the light-emitting part 14 (e.g., the valid reflected lightR1′ produced by the light R1 being reflected at the blood vessel BV,shown in FIG. 1A).

Design of a Reflecting Part Having a Reflecting Surface that Uses a Partof a Spherical Surface

Next, a design of the reflecting part having the reflecting surface thatuses a part of a spherical surface will be described with reference toFIGS. 6 through 16. FIGS. 6A and 6B are drawings representing parametersrelating to designing the reflecting part having the reflecting surfacethat uses a part of a spherical surface, and to an example of a methodfor designing the reflecting part.

In the example shown in FIG. 6A, a mutually perpendicular x-axis,y-axis, and z-axis are shown in order to define a three-dimensionalspace. The z-axis is defined as an optical axis (i.e., a main opticalaxis). A point of intersection between the z-axis and the reflectingsurface of the reflecting part 18 is defined as an origin (i.e., asurface origin) m.

The aperture diameter of the reflecting surface of the reflecting part18 is represented by cp. The reflecting surface of the reflecting part18 includes a part of a spherical surface, which is a quadric surface.In the example shown in FIG. 6A, the reflecting surface includes asubstantially hemispherical surface, which is a part of a sphericalsurface.

A focal point of the reflecting part 18 (i.e., a focal point of alight-collecting mirror including the reflecting surface) is f. When alight beam LG that is parallel to the optical axis (i.e., the z-axis) isincident on the reflecting part 18, the light is reflected on thereflecting part 18 and collects at the focal point f. The distancebetween the origin m and the focal point f is the focal distance df.

A distance that is twice that of the focal distance df is equivalent tothe curvature radius r of the reflecting surface. Specifically, thefocal distance df is equal to r/2. Also, in FIG. 6A, point p representsa center point of a spherical surface forming the reflecting surface ofthe reflecting part 18.

The height of the reflecting surface of the reflecting part 18 isrepresented by h. The height h is established by a distance from thesecond surface (i.e., the surface on the side towards the reflectingpart 18) of the substrate 11 to the origin (i.e., the surface origin) m.Specifically, the height h of the reflecting surface represents thedistance between a point m of intersection between the optical axis(i.e., the z-axis) and the reflecting surface (i.e., the surface originm) and the second surface of the substrate 11 (i.e., the main surface ofthe substrate 11 that is arranged on a side towards the reflectingsurface; the front surface of the substrate 11). The height h of thereflecting surface is unambiguously established in correspondence withthe curvature radius r and the aperture diameter φ of the reflectingsurface. Also, Δh is used to represent the difference between the heighth of the reflecting surface and the curvature radius r of the reflectingsurface. The difference Δh (may be referred to simply as Ah) isestablished by a distance from the second surface of the substrate 11 tothe center point p of the spherical surface forming the reflectingsurface.

Also, as described above, the height of the spacer member 19-1 in theprotecting part 19 (i.e., a spacing between the substrate 11 and asurface of the contact member 19-2 that is opposite the contact surfaceSA) is represented by δ, and the thickness of the contact member 19-2 isrepresented by t.

A simulation will now be made for an instance in which each of theaperture diameter φ of the reflecting part 18, the height δ of thespacer member 19-1 (i.e., the spacing between the substrate 11 and thesurface of the contact member 19-2 that is opposite the contact surfaceSA), and the thickness t of the contact member 19-2 is fixed to apredetermined value, and Δh or the focal distance df of the reflectingpart 18 is varied. FIG. 6B is a drawing representing how the curvatureradius r of the reflecting surface (i.e., the spherical surface formingthe reflecting surface) and the shape of the reflecting surface of thereflecting part 18 vary in such an instance.

In FIG. 6B, Δh (i.e., the difference between the height h of thereflecting surface and the curvature radius r of the reflecting surface)is set to Δh1, Δh2, and Δh3. Correspondingly, the curvature radius r ofthe reflecting surface changes from r1 to r2 and r3. Specifically, thecurvature radius is r1 at Δh1, the curvature radius is r2 at Δh2, andthe curvature radius is r3 at Δh3.

Since the focal distance df of the reflecting part 18 (i.e., areflecting light-collecting mirror) is half the curvature radius r, whencurvature radius r changes, the focal distance df changes incorrespondence with the curvature radius r. When the curvature radius isr1, the focal distance is represented by df1, and the focal point f ofthe reflecting part 18 is represented by f1. When the curvature radiusis r2, the focal distance is represented by df2, and the focal point fof the reflecting part 18 is represented by f2. When the curvatureradius is r3, the focal distance is represented by df3, and the focalpoint f of the reflecting part 18 is represented by f3.

In FIG. 6(B), when the curvature radius r changes, the shape of thereflecting surface including a spherical surface also changes incorrespondence with the change in curvature radius r. Specifically,since φ is constant, the position of each of points a and b defining theaperture diameter is fixed; therefore, when the curvature radius rchanges, the height h of the reflecting surface including a sphericalsurface also changes in accordance with the change in the curvatureradius r. In FIG. 6B, the shape of the reflecting surface when thecurvature radius r is equal to r1 is represented by 18 a. The shape ofthe reflecting surface when the curvature radius r is equal to r2 isrepresented by 18 b. The shape of the reflecting surface when thecurvature radius r is equal to r3 is represented by 18 c. Thus changingΔh makes it possible to change the three-dimensional shape and theheight of the reflecting surface.

Although according to the above description, the three-dimensional shapeand height of the reflecting surface are changed by changing the Δh, theshape of the reflecting surface can also be changed by changing thefocal distance df. Specifically, when the φ of the reflecting surface isa fixed value (i.e., already known), changing, e.g., the focal distancedf of the reflecting part 18 (i.e., the reflective optical system)changes the curvature radius r of (the spherical surface forming) thereflecting surface. When the curvature radius r changes, the differenceΔh between the height h and the curvature radius r of the reflectingsurface changes. The focal distance df of the reflecting surface and thedifference Δh between the height h and the curvature radius r of thereflecting surface have a one-to-one correspondence relationship. Whenthe focal distance df increases, Δh also increases. When the focaldistance df of the reflecting part 18 is established, Δh is established.

The curvature radius r of the contact surface forming the reflectingsurface (i.e., the curvature radius of the reflecting surface) can berepresented using the following Equation 1 (refer to right-angledtriangle indicated by thick arrows in FIG. 6A).

Mathematical formula 1r=√{square root over ({Δh ²+(φ/2)²})}  (1)

Focusing, e.g., on a right-angled triangle shown at the lower left sideof FIG. 6B shaded with diagonal lines, it can be seen, using thePythagorean theorem, that the curvature radius r3 can be represented bythe following Equation 2.

Mathematical formula 2r3=√{square root over ({Δh3²+(φ/2)²})}  (2)

Therefore, when a preferred focal distance of the reflecting surface isestablished, the curvature radius r can be unambiguously establishedusing the above Equation 1, and the spherical surface forming thereflecting surface is established. Also, since the aperture diameter φof the reflecting surface (i.e., the diameter of the outercircumferential circle of the reflecting surface with respect to theplan view) is fixed (i.e., already known), the height h of thereflecting surface is unambiguously established. Specifically, when φ isestablished, a slicing position of the spherical surface (i.e., aposition at which the spherical surface is sliced along an x-y plane) iscorrespondingly established, whereby the three-dimensional shape andheight of the reflecting surface are unambiguously established.

The above-described method for designing a reflective optical system canbe used to design the reflecting part 18 so as to reduce theonce-reflected light and the twice-reflected light (which are bothinvalid directly reflected light) shown in FIG. 1B.

A Simulation of Behavior of Reflected Light in an Instance in whichFocal Distance Df or Difference Δh is Changed

A description will now be given for, e.g., a result of a simulation of abehavior of reflected light in an instance in which the focal distancedf or the difference Δh is changed, with reference to FIGS. 7 through16. FIG. 7 is a drawing representing an example of dimensions of mainconfigurations in the biological information detector (the dimensionsare not limited to those described in the example below). As shown inFIG. 7, the aperture diameter φ is set to 4.4 mm, the height δ of thespacer member 19-1 of the protecting part 19 (or, the spacing) is set to0.53 mm, the thickness t of the contact member 19-2 (i.e., the thicknessof the glass) is set to 0.4 mm.

As shown in FIG. 7, the thickness to of the light-receiving part 16 is,e.g., 0.28 mm, the thickness tb of a bottom part of the reflector 20 is,e.g., 0.08 mm, the thickness tc of the light-emitting part 14 is, e.g.,0.08 mm, and the maximum height td of the reflector 20 is, e.g., 0.2 mm.

The actual thickness te of the substrate 11 (including thelight-transmitting film, i.e., the light-transmitting resist films 11-1and 11-2) is, e.g., about 0.07 mm. However, since the substrate 11 issufficiently thin, and, as described above, the light-transmittingresist film maintains smoothness and reduces the difference inrefractive index in relation to air, the thickness te of the substrate11 is ignored in the simulation of the behavior of the reflected light(i.e., te is considered zero). Also, the reflecting surface of thereflecting part 18 includes a part of a spherical surface, which is aquadric surface, as described above.

The refractive index of glass forming the protecting part 19 is, e.g.,1.52. The refractive index of polyamide forming the substrate 11 is,e.g., 1.7. Polyarylate (with a refractive index of 1.61) may also beused as a material for the transparent substrate.

The behavior of directly reflected light (i.e., invalid light or invalidreflected light) and the behavior of light having biological information(i.e., valid light or valid reflected light) in an instance in which thefocal distance df of the reflecting surface (i.e., a spherical mirror)(or, the difference Δh between the height of the reflecting surface andthe curvature radius of the reflecting surface) is changed (with otherparameters being fixed) will now be discussed in relation to thebiological information detector 200 shown in FIG. 7.

FIGS. 8A and 8B are drawings used to describe a behavior of directlyreflected light (i.e., invalid light) in an instance in which df=1.18 mm(Δh=0.4 m). As shown in FIG. 8B, the reflecting surface of thereflecting part 18 is a substantially hemispherical surface. In FIG. 8A,the reflecting surface 18-1 of the reflecting part 18 and the spacermember 19-1 are shown, not as a cross-section, but as a shape havingspatial depth (this also applies to subsequent drawings).

In FIG. 8A, trajectories of directly reflected light (i.e., invalidlight), produced by light emitted by the light-emitting part 14 (notincluding light reflected on the reflector or another member) reflectingon a side of the contact member 19-2 of the protecting part 19 towardsthe contact surface SA (i.e., the contact surface SA or a vicinitythereof) are shown by solid arrows.

As can be seen from FIG. 8A, there is a high probability ofonce-reflected light, which is light emitted by the light-emitting part14 reflecting once on the side of the contact member 19-2 towards thecontact surface SA, being incident on the light-receiving region (i.e.,the light-receiving surface) 16-1 of the light-receiving part 16.Specifically, there is a tendency towards a higher ratio of the amountof once-reflected incident light (i.e., incident light resulting fromthe once-reflected light being reflected by the reflecting surface andbeing incident on the light-receiving part 16) in relation to the totalamount of light received at the light-receiving part 16.

For example, once-reflected light A1 reflects once at a point N1 on thecontact member 19-2 on the side towards the contact surface SA. Theonce-reflected light passes through the substrate 11, reflects on thereflecting part 18, and reaches the light-receiving region 16-1 of thelight-receiving part 16 in a direct manner (i.e., without undergoingcomplex reflections or scattering). Once-reflected light A2 reflectsonce at a point N2 on the contact member 19-2 on the side towards thecontact surface SA. The once-reflected light passes through thesubstrate 11, reflects on the reflecting part 18, and reaches (i.e., isincident on) the light-receiving region 16-1 of the light-receiving part16 in a direct manner. Also, once-reflected light A3 reflects once at apoint N3 on the contact member 19-2 on the side towards the contactsurface SA. The once-reflected light passes through the substrate 11,reflects on the reflecting part 18, and reaches (i.e., is incident on)the light-receiving region 16-1 of the light-receiving part 16 in adirect manner.

Meanwhile, as described above using FIG. 1A, reflected light R1′reflected at the blood vessel BV (i.e., valid reflected light havingbiological information) is incident on the light-receiving region (i.e.,the light-receiving surface) 16-1 of the light-receiving part 16.

Next, a description will be made with reference to FIG. 9. FIG. 9 is adrawing used to describe a behavior of directly reflected light in aninstance in which df=1.278 mm (Δh=1.3 m). Trajectories of directlyreflected light (i.e., invalid light), produced by light emitted by thelight-emitting part 14 reflecting on a side of the contact member 19-2of the protecting part 19 towards the contact surface SA (i.e., thecontact surface SA or a vicinity thereof) in the example shown in FIG. 9are shown by solid arrows.

As can be seen in FIG. 9, there are substantially no instances ofonce-reflected light, which is the light emitted by the light-emittingpart 14 reflecting once on the side of the contact member 19-2 towardsthe contact surface SA, being incident on the light-receiving region(i.e., the light-receiving surface) 16-1 of the light-receiving part 16.There are also substantially no instances of twice-reflected light,which is the light emitted by the light-emitting part 14 reflectingtwice on the side of the contact member 19-2 towards the contact surfaceSA, being incident on the light-receiving region (i.e., thelight-receiving surface) 16-1 of the light-receiving part 16.

Specifically, there is a tendency for the ratio of the amount ofincident light resulting from the directly reflected light (includingonce-reflected light and twice-reflected light) being reflected by thereflecting surface and being incident on the light-receiving part 16(i.e., directly reflected incident light) in relation to the totalamount of light received at the light-receiving part 16 to besignificantly minimized.

Meanwhile, as described above using FIG. 1A, reflected light R1′reflected at the blood vessel BV (i.e., valid reflected light havingbiological information) arrives at (i.e., is incident on) thelight-receiving region (i.e., the light-receiving surface) 16-1 of thelight-receiving part 16.

Next, a description will be made with reference to FIG. 10. FIG. 10 is adrawing used to describe a behavior of directly reflected light in aninstance in which df=1.556 mm (Δh=2.2 m). Trajectories of directlyreflected light (i.e., invalid light), produced by light emitted by thelight-emitting part 14 reflecting on a side of the contact member 19-2of the protecting part 19 towards the contact surface SA (i.e., thecontact surface SA or a vicinity thereof) in the example shown in FIG.10 are shown by solid arrows.

As can be seen in FIG. 10, there is a high probability of thetwice-reflected light, which is the light emitted by the light-emittingpart 14 reflecting twice on the side of the contact member 19-2 towardsthe contact surface SA, being incident on the light-receiving region(i.e., the light-receiving surface) 16-1 of the light-receiving part 16.

Specifically, there is a tendency towards a higher ratio of the amountof incident light resulting from the twice-reflected light, which is adirectly reflected light (i.e., invalid light), being reflected by thereflecting surface and being incident on the light-receiving part 16(i.e., twice-reflected incident light) in relation to the total amountof light received at the light-receiving part 16.

For example, twice-reflected light A4 is reflected twice, at points N4and N5 on the contact member 19-2 on the side towards the contactsurface SA. The twice-reflected light passes through the substrate 11,reflects on the reflecting part 18, and reaches (i.e., is incident on)the light-receiving region 16-1 of the light-receiving part 16 in adirect manner. Also, twice-reflected light A5 reflects twice at pointsN6 and N7 on the contact member 19-2 on the side towards the contactsurface SA. The twice-reflected light passes through the substrate 11,reflects on the reflecting part 18, and reaches (i.e., is incident on)the light-receiving region 16-1 of the light-receiving part 16 in adirect manner. Also, twice-reflected light A6 reflects twice at pointsN8 and N9 on the contact member 19-2 on the side towards the contactsurface SA. The twice-reflected light passes through the substrate 11,reflects on the reflecting part 18, and reaches (i.e., is incident on)the light-receiving region 16-1 of the light-receiving part 16 in adirect manner.

Meanwhile, as described above using FIG. 1A, reflected light R1′reflected at the blood vessel BV (i.e., valid reflected light havingbiological information) arrives at (i.e., is incident on) thelight-receiving region (i.e., the light-receiving surface) 16-1 of thelight-receiving part 16.

A simulation of a behavior of the directly reflected light wasrepeatedly performed, and a correlation between changes in the focaldistance of the reflecting surface and the ratio of directly reflectedlight (i.e., invalid light) incident on the light-receiving part wasstudied. A result is shown in FIG. 11. FIG. 11 is a drawing representinga change in a ratio (%) of the amount of directly reflected lightincident on the light-receiving part (photodiode) in relation to thetotal amount of light received at the light-receiving part 16 in aninstance in which the focal distance df is gradually increased where theaperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm.

In FIG. 11, gradually increasing the focal distance df of the reflectingsurface results first in a focal distance range FA (i.e., a range offocal distance df from 1.1 to 1.2) in which a ratio, with respect to anamount of light received at the light-receiving region 16-1 of thelight-receiving part 16, of light beams that reflect once at the contactmember 19-2 of the protecting part 19 on a side towards the contactsurface SA, then reflect again at the reflecting surface, and arrive atthe light-receiving region of the light-receiving part in a directmanner, is higher than a predetermined first threshold value(approximately equal to 0%). The focal distance range FA is defined as afirst focal distance range. The first focal distance range is a focaldistance range that corresponds to single reflections.

Further increasing the focal distance df of the reflecting surfaceresults next in a focal distance range FB (i.e., a range of focaldistance df from 1.2 to 1.41) in which almost no once-reflected lightreaches the light-receiving region of the light-receiving part 16. Thefocal distance range FB is defined as a second focal distance range. Thesecond focal distance range is a focal distance range within whichincidence of directly reflected light on the light-receiving part 16 isminimized.

Further increasing the focal distance df of the reflecting surfaceresults next in a focal distance range FC (i.e., a range of focaldistance df from 1.41 to 1.7) in which a ratio, with respect to anamount of light received at the light-receiving region of thelight-receiving part 16, of light beams that reflect twice at thecontact member 19-2 of the protecting part 19 on a side towards thecontact surface SA, then reflects again at the reflecting surface, andarrives at the light-receiving region 16-1 of the light-receiving part16 in a direct manner, is higher than a predetermined second thresholdvalue (approximately equal to 0%). The focal distance range FC isdefined as a third focal distance range. The third focal distance rangeis a focal distance range that corresponds to double reflections.

Next, a description will be given for a behavior of reflected lightincluding, in addition to invalid light, valid light having biologicalinformation (i.e., valid reflected light; light R1′ shown in FIG. 1A.The behavior of reflected light including invalid light and valid lightis revealed by examining the change in the S/N of a biologicalinformation detection signal (e.g., pulse information detection signal)outputted from the light-receiving part 16. The behavioral tendency ofinvalid light (i.e., invalid reflected light) has been revealed in FIG.11.

Therefore, a tendency with which the S/N of the detection signaloutputted from the light-receiving part 16 changes can be compared withthe behavioral tendency of invalid light (i.e., invalid reflected light)shown in FIG. 11 to identify a behavioral tendency of valid light (i.e.,valid reflected light) having biological information. For example, ifthere appears a focal distance range with an increasing S/N in thedetection signal within a focal distance range in which the amount ofinvalid light (i.e., noise N) reaching the light-receiving region 16-1of the light-receiving part 16 is significantly minimized indicates thatthe amount of valid light (i.e., signal S) is increasing in the focaldistance range.

FIG. 12 is a drawing representing an example of a change in a ratio of apulse signal (%) relative to a pulse information detection signal (i.e.,all signal including pulse signal having pulse information as well asnoise) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm.

As can be seen in FIG. 12, the S/N of the detection signal peaks at avicinity of a focal distance df of 1.28. The focal distance dfcorresponding to the peak (i.e., df=1.28) is within the second focaldistance range FB (i.e., a range of focal distance df from 1.2 to 1.41)shown in FIG. 11.

Also, it can be seen that the S/N of the detection signal in each of thefirst focal distance range FA (i.e., a range of focal distance df from1.1 to 1.2) and the third focal distance range FC (i.e., a range offocal distance df from 1.41 to 1.7) shown in FIG. 11 is generally lowerthan the S/N of the detection signal in the second focal distance rangeFB (i.e., a range of focal distance df from 1.2 to 1.41).

As described above, the second focal distance range FB is a focaldistance range in which directly reflected light (i.e., invalid light)is significantly minimized. Therefore, the fact that the S/N of thedetection signal in the second focal distance range FB is higher than inother focal distance ranges (i.e., FA and FC) indicates that,specifically, the ratio of valid light (i.e., valid reflected light) inthe second focal distance range FB is higher (i.e., more valid light isincident on the light-receiving region 16-1 of the light-receiving part16) than in the other focal distance ranges (i.e., the first focaldistance range FA and the third focal distance range FC).

Specifically, in the second focal distance range FB (i.e., a range offocal distance df from 1.2 to 1.41), in addition to the effect ofminimizing the incidence of directly reflected light (i.e., invalidlight) on the light-receiving region 16-1 of the light-receiving part16, an effect of increasing the amount of valid light (i.e., validreflected light; light R1′ in FIG. 1A) having pulse rate information asbiological information can be obtained. Therefore, setting the focaldistance df of the reflecting surface 18-1 of the reflecting part 18within the focal distance range FB makes it possible to increase the S/Nof the detection signal corresponding to detection of the pulse rate asbiological information. Specifically, improving the S/N of the detectionsignal makes it possible to perform detection with a higher degree ofaccuracy. In particular, setting the focal distance df of the reflectingsurface 18-1 of the reflecting part 18 at a focal distance correspondingto a vicinity of the peak value of the S/N of the detection signal makesit possible to maximize the detection accuracy.

Although in the example described above, optical characteristics of thereflecting part were analyzed using the focal distance df as aparameter, a similar result can be obtained in an instance in which Δhis used as a parameter.

FIG. 13 is a drawing representing a change in the ratio (%) of theamount of directly reflected light (i.e., invalid light) incident on thelight-receiving part (photodiode) in an instance in which Δh isgradually increased where the aperture diameter φ=4.4 mm, t=0.4 mm, andδ=0.53 mm. As described above, there is a one-to-one correspondencerelationship between the focal distance df and the difference Δh betweenthe height h and the curvature radius r of the reflecting surface; whenone increases, the other also increases. In the example shown in FIG.13, the change in the ratio (%) of the amount of directly reflectedlight is examined using Δh as a parameter (i.e., a variable).

In FIG. 13, there exist a Δh range QA corresponding to singlereflections (i.e., Δh is within a range of 0.1 to 1.0, in which theratio is equal to or above 1%; first Δh range); a Ah range QB in whichincidence of the directly reflected light on the light-receiving part isminimized (i.e., Δh is within a range of 1.0 to 1.6, in which the ratiois equal to or below 1%; second Δh range); and a Δh range QCcorresponding to double reflections (Δh is within a range of from 1.6 to2.8, in which the ratio is above 1%; third Δh range). In the exampleshown in FIG. 13, the predetermined first and second threshold valuesare both 1%.

FIG. 14 is a drawing representing another example of a change in theratio of the pulse signal (%) relative to a pulse information detectionsignal (i.e., all signals including pulse signal having pulseinformation as well as noise) in an instance in which Δh is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.4 mm, and δ=0.53 mm.As can be seen in FIG. 14, the S/N of the detection signal outputtedfrom the light-receiving part 16 peaks at a vicinity of a Δh of 1.28. Δhcorresponding to the peak (i.e., Δh=1.28) is within the Ah range QBshown in FIG. 13, in which incidence of directly reflected light on thelight-receiving part is minimized (i.e., a range of Δh from 1.0 to 1.6;the second Δh range).

It can also be seen that the S/N of the detection signal in each of theth range QA corresponding to single reflections (i.e., a range of Δhfrom 0.1 to 1.0; the first Δh range) and the Δh range QC correspondingto double reflections (i.e., a range of Δh from 1.6 to 2.8; the third Δhrange) shown in FIG. 13 is generally lower than the S/N of the detectionsignal in the second th range QB. Specifically, it can be seen that inthe second Δh range QB (i.e., a range of Δh from 1.0 to 1.6), inaddition to the effect of minimizing the incidence of directly reflectedlight on the light-receiving region 16-1 of the light-receiving part 16,an effect of increasing the incidence amount of valid light having pulserate information can be obtained, whereby the S/N of the pulse rateinformation detection signal increases (i.e., the S/N of the detectionsignal improves) relative to other Δh regions (i.e., the first Δh rangeQA and the third Δh range QC).

Therefore, setting Δh within the second Δh range QB makes it possible toimprove the S/N of the detection signal corresponding to detection ofthe pulse rate as biological information. Specifically, the S/N of thedetection signal can be improved, thereby making it possible to performdetection with a higher degree of accuracy. In particular, setting Δh ata value corresponding to a vicinity of the peak value of the S/N of thedetection signal makes it possible to maximize the detection accuracy.

FIGS. 15 and 16 represent results obtained when dimension conditionsthat represent preconditions are partially changed and a similarsimulation is performed.

Specifically, FIG. 15 is a drawing representing a change in the ratio(%) of the amount of directly reflected light incident on thelight-receiving part (photodiode) in an instance in which the focaldistance df is gradually increased where the aperture diameter φ=3.6 mm,t=0.4 mm, and δ=0.53 mm. In the example shown in FIG. 15, the aperturediameter φ has been changed from 4.4 mm (as in the example describedabove) to 3.6 mm.

In the example shown in FIG. 15, it can again be seen that a first focaldistance range FA′ (a range of focal distance df from 0.9 to 0.99), asecond focal distance range FB′ (a range of focal distance df from 0.99to 1.22), and a third focal distance range FC′ (a range of focaldistance df from 1.22 to 1.49) are present.

FIG. 16 is a drawing representing a change in the ratio (%) of theamount of directly reflected light incident on the light-receiving part(photodiode) in an instance in which the focal distance df is graduallyincreased where the aperture diameter φ=4.4 mm, t=0.3 mm, and δ=0.3 mm.In the example shown in FIG. 16, the thickness t of the contact member19-2 has been changed from 0.4 mm (as in the example described above) to0.3 mm, and the height δ (i.e., the spacing) of the spacer member 19-1has been changed from 0.53 (as in the example described above) to 0.3mm.

In the example shown in FIG. 16, a first focal distance range FA″ (arange of focal distance df from 1.1 to 1.14), a second focal distancerange FB″ (a range of focal distance df from 1.14 to 1.28), and a thirdfocal distance range FC″ (a range of focal distance df from 1.28 to1.62) are again present.

In an instance in which any of the aperture diameter φ, the thickness tof the contact member 19-2, and the height δ (i.e., the spacing) of thespacer member 19-1 has been changed, the second focal distance rangethus appears between the focal distance range and the third focaldistance range. Therefore, it can be seen that a main parameter that hasthe largest effect on the behavior of directly reflected light of suchdescription is focal distance df (or Δh). Therefore, using the focaldistance df (or Δh) as a design parameter is effective when designingthe reflecting part 18 to realize preferable reflective characteristics.

When such observations are taken into consideration, the focal distancedf of the reflecting surface of the reflecting part 18 is preferably setwithin the second focal distance range FB (FB′, FB″), which is betweenthe first focal distance range FA (FA′, FA″) and the third focaldistance range FC (FC′, FC″).

As described above, when the focal distance df of the reflecting surfaceis established, the curvature radius of the spherical surface formingthe reflecting surface is established. The spherical surface istherefore unambiguously established. Also, since the aperture diameterof the reflecting surface is already known, the position at which thespherical surface is sliced along the x-y plane is unambiguouslyestablished, and height h of the reflecting surface including a part ofthe spherical surface is thereby established. The three-dimensionalshape and height of the reflecting surface of the reflecting part 18 isthereby unambiguously established.

Using the design method described above to adjust the reflectivecharacteristics of the reflecting part 18 makes it possible to minimizeincidence of the once-reflected light (i.e., invalid light) and thetwice-reflected light (i.e., invalid light) on the light-receivingregion 16-1 of the light-receiving part 16 and increase the probabilityof valid reflected light, having biological information, being incidenton the light-receiving region 16-1 of the light-receiving part 16. It isthereby possible to minimize adverse effects (e.g., a decrease in theS/N of the detection signal outputted from the light-receiving part 16)of light reflected on the contact member 19-2 on a side towards thecontact surface SA (i.e., directly reflected light).

Second Embodiment

In the present embodiment, the reflecting surface of the reflecting partincludes a part of a paraboloid, which is a quadric surface. Whereas inthe previous embodiment, the reflecting surface of the reflecting partwas constituted using a spherical surface, which is a quadric surface,the reflecting surface can also be constituted using a non-sphericalsurface (i.e., a paraboloid).

A paraboloid of revolution can be used as the paraboloid. The paraboloidof revolution is a quadric surface obtained by revolving a parabola,using a z-axis, which is an axis of symmetry, as an axis of revolution,where an z-axis, among mutually perpendicular x-, y-, and z-axes thatdefine a 3-dimensional space, is an optical axis (i.e., a curved surfacerepresented by a quadratic equation with three unknowns of x, y, and z).

FIGS. 17A and 17B are drawings used to describe a reflecting surfaceincluding a part of a paraboloid (i.e., a paraboloid mirror). As shownin FIG. 17B, when the z-axis among the mutually perpendicular x-, y-,and z-axes that define a 3-dimensional space is the optical axis (i.e.,main optical axis), the paraboloid forming the reflecting surface may bea paraboloid of revolution having the z-axis as an axis of revolution. Apoint of intersection between the z-axis and the paraboloid ofrevolution is defined as an origin (surface origin) m.

In an instance in which r represents the curvature radius of a sphericalsurface CQ in contact with the origin m, the following Equation 3 istrue with respect to the paraboloid of revolution, as shown in FIGS. 17Aand 17B.

Mathematical Formula 3z=(½r)·(x ² +y ²)  (3)

The outer circumferential shape of the reflecting surface 18-1 withrespect to the plan view is circular, as with the previous embodiment,and the diameter φ of the circle (i.e., the aperture diameter of thereflecting surface) is set to a predetermined value. When the aperturediameter φ of the reflecting surface is already known, the focaldistance df of the reflecting surface and the curvature radius r of thespherical surface CQ in contact with the origin m of the paraboloidforming the reflecting surface have a one-to-one correspondencerelationship. Therefore, when a preferable focal distance df isestablished, the curvature radius r of the spherical surface in contactwith the origin m is established, and the paraboloid of revolution isunambiguously established by the above Equation 3. Also, since theaperture diameter φ of the reflecting surface is already known, aposition at which the paraboloid of revolution is sliced along an x-yplane is thereby established, and the height h of the reflecting surfaceis unambiguously established. The three-dimensional shape (and height)of the reflecting surface is thereby unambiguously established.

Next, a behavior of directly reflected light (i.e., invalid light) inwhich the focal distance df of the reflecting surface 18-1 (i.e., aparaboloid mirror) is changed (with other parameters being fixed) willnow be discussed with reference to FIGS. 18 through 20.

FIG. 18 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 0.7 mm where the aperture diameterφ=4.4 mm, the thickness t of contact member 19-2=0.4 mm, and the height(spacing) δ of the spacer member 19-1=0.53. The reflecting surface 18-1of the reflecting part 18 shown in FIG. 18 includes a part of aparaboloid. In FIG. 18, the reflecting surface of the reflecting part 18is shown, not as a cross-section, but as a shape having spatial depth(this also applies to subsequent drawings).

In FIG. 18, trajectories of directly reflected light (i.e., invalidlight), produced by light emitted by the light-emitting part 14 (notincluding light reflected on the reflector or another member) reflectingon a side of the contact member 19-2 of the protecting part 19 towardsthe contact surface SA (i.e., the contact surface SA or a vicinitythereof) are shown by solid arrows.

As can be seen from FIG. 18, there is a high probability ofonce-reflected light, which is light emitted by the light-emitting part14 reflecting once on the side of the contact member 19-2 towards thecontact surface SA, being incident on the light-receiving region (i.e.,the light-receiving surface) 16-1 of the light-receiving part 16.Specifically, there is a tendency towards a higher ratio of the amountof once-reflected incident light in relation to the total amount oflight received at the light-receiving part 16.

FIG. 19 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 1.0 mm where the aperture diameterφ=4.4 mm, the thickness t of the contact member 19-2=0.4 mm, and theheight (spacing) δ of the spacer member 19-1=0.53.

As can be seen in FIG. 19, there are substantially no instances ofonce-reflected light, which is the light emitted by the light-emittingpart 14 reflecting once on the side of the contact member 19-2 towardsthe contact surface SA, being incident on the light-receiving region(i.e., the light-receiving surface) 16-1 of the light-receiving part 16.There are also substantially no instances of twice-reflected light,which is the light emitted by the light-emitting part 14 reflectingtwice on the side of the contact member 19-2 towards the contact surfaceSA, being incident on the light-receiving region (i.e., thelight-receiving surface) 16-1 of the light-receiving part 16. Meanwhile,as with the example shown in FIG. 1A described above, reflected lightfrom the blood vessel (i.e., valid reflected light having biologicalinformation) is incident on the light-receiving region (i.e., thelight-receiving surface) 16-1 of the light-receiving part 16.

FIG. 20 is a drawing used to describe a behavior of directly reflectedlight when the focal distance df is 1.3 mm where the aperture diameterφ=4.4 mm, the thickness t of the contact member 19-2=0.4 mm, and theheight (spacing) δ of the spacer member 19-1=0.53.

As can be seen in FIG. 20, there is a high probability of thetwice-reflected light, which is the light emitted by the light-emittingpart 14 reflecting twice on the side of the contact member 19-2 towardsthe contact surface SA, being incident on the light-receiving region(i.e., the light-receiving surface) 16-1 of the light-receiving part 16.Specifically, there is a tendency towards a higher ratio of the amountof twice-reflected incident light in relation to the total amount oflight received at the light-receiving part 16.

A simulation of a behavior of the directly reflected light wasrepeatedly performed, and a correlation between changes in the focaldistance of the reflecting surface and the ratio of directly reflectedlight incident on the light-receiving part 16 was studied. A result isshown in FIG. 21. FIG. 21 is a drawing representing a change in theratio (%) of the amount of directly reflected light incident on thelight-receiving part (photodiode) in an instance in which the focaldistance df is gradually increased where the aperture diameter φ=4.4 mm,t=0.4 mm, and δ=0.53 mm.

In FIG. 21, gradually increasing the focal distance df of the reflectingsurface results first in a first focal distance range FA (i.e., a rangeof focal distance df from 0.55 mm to 1.0 mm), as with theabove-described instance in which a reflecting surface including a partof a spherical surface is used. Next, a second focal distance range FB(i.e., a range of focal distance df from 1.0 mm to 1.15 mm) appears.

In the focal distance range FB, the ratio of the amount of directlyreflected light incident on the light-receiving part is minimized so asto be equal to or below 1% (the first and second threshold values, usedas predetermined threshold values in the present example to determinewhether the amount of reflected light is high or low, are 1%). Also, theratio of directly reflected light is almost zero in a vicinity of thefocal distance df of 1.1.

Further increasing the focal distance df of the reflecting surfaceresults in a third focal distance range FC (i.e., a range of focaldistance df from 1.15 mm to 1.55 mm).

When such observations are taken into consideration, the focal distanceof the reflecting surface (i.e., the paraboloid mirror) of thereflecting part 18 is preferably set within the second focal distancerange FB, which is between the first focal distance range FA and thethird focal distance range FC. The decrease in S/N of the detectionsignal outputted from the light-receiving part 16, caused by thedirectly reflected light (i.e., invalid light), is thereby minimized. Asa result, the detection accuracy increases. Also, since the ratio ofdirectly reflected light is almost zero in the vicinity of the focaldistance df of 1.1, the focal distance is most preferably set in thevicinity of 1.1.

Also, although not shown, studying a change in S/N of the detectionsignal has confirmed that the amount of received valid light (i.e.,valid reflected light) having biological information increases in thesecond focal distance range FB.

Therefore, setting the focal distance df within the second focaldistance range makes it possible to increase the S/N of the detectionsignal corresponding to detection of the pulse rate as biologicalinformation. Specifically, improving the S/N of the detection signalmakes it possible to perform detection with a higher degree of accuracy.In particular, setting the focal distance df to a value corresponding toa vicinity of the peak value of the S/N of the detection signal (i.e.,1.1) makes it possible to maximize the detection accuracy.

As described above, when the focal distance df of the reflecting surfaceis established, the three-dimensional shape and height of the reflectingsurface are unambiguously established. Therefore, using the designmethod described above makes it possible to obtain a reflecting part 18having preferable reflective characteristics with which the effect ofdirectly reflected light can be reduced.

Third Embodiment

In the present embodiment, a description will be given for a biologicalinformation measuring device including the biological informationdetector. FIG. 22 is a drawing representing an external appearance of anexample of a biological information measuring device (i.e., a wristpulse rate monitor) including the biological information detector. Thebiological information measuring device 300 may further include awristband 150 capable of attaching a housing member 160 for thebiological information detector 200 to an arm (or specifically, awrist), which is the detection site 1, of the test subject (i.e., humanbody) 2.

In the example shown in FIG. 22, the biological information is the pulserate, and the pulse rate (i.e., “72”), which is a measurement result, isdisplayed on a display part 165 provided to the biological informationmeasuring device 300. The biological information measuring device 300also functions as a wristwatch. The time (e.g., “8:45 am”) is displayedon the display part 165 provided to the biological information measuringdevice 300.

Although not shown, an opening part is provided to a back cover of thehousing member 160 of the biological information measuring device 300that also functions as the wristwatch, and the protecting part (i.e.,protective case) 19 described above is exposed in the opening part.

FIG. 23 is a drawing representing an example of an internalconfiguration of the biological information measuring device. Thebiological information measuring device 300 includes the biologicalinformation detector 200 shown in FIG. 1 and other drawings, and abiological information measuring part 202 for measuring biologicalinformation from a light reception signal generated by thelight-receiving part 16 of the biological information detector. In FIG.23, a portion that functions as a clock is omitted. The biologicalinformation detector 200 may have the light-emitting part 14, thelight-receiving part 16, and a control circuit 161 for controlling thelight-emitting part 14. The biological information detector 200 mayfurther have an amplification circuit 162 for amplifying the lightreception signal from the light-receiving part 16. The biologicalinformation detector 200 may further have an acceleration detecting part166.

The biological information measuring part 202 may have an A/D conversioncircuit 163 for performing A/D conversion of the light reception signalfrom the light-receiving part 16, and a pulse rate computation circuit164 for computationally obtaining the pulse rate. The biologicalinformation measuring device 300 may further have the display part 165for displaying the pulse rate.

As described above, the biological information detector 200 may have theacceleration detecting part 166; in such an instance, the biologicalinformation measuring part 202 may have an A/D conversion circuit 167for performing A/D conversion on a detection signal from theacceleration detecting part 166, and a digital signal processing circuit168 for processing a digital signal. The configuration of the biologicalinformation measuring device shown in FIG. 23 is given by way ofexample, but is not limited to the configuration shown.

The pulse rate computation circuit 164 may be, e.g., an MPU (i.e., amicroprocessing unit) of an electronic device installed with thebiological information detector 200. The control circuit 161 drives thelight-emitting part 14. The control circuit 161 is, e.g., a constantcurrent circuit, delivers a predetermined voltage (e.g. 6 V) to thelight-emitting part 14 via a protective resistance, and maintains acurrent flowing to the light-emitting part 14 at a predetermined value(e.g. 2 mA). The control circuit 161 is capable of driving thelight-emitting part 14 in an intermittent manner (e.g. at 128 Hz) inorder to reduce consumption current. The control circuit 161 is formedon, e.g., a motherboard (not shown), and wiring between the controlcircuit 161 and the light-emitting part 14 is formed, e.g., on thesubstrate 11.

The amplification circuit 162 shown in FIG. 23 is capable of removing aDC component from the light reception signal (i.e., an electricalcurrent) generated in the light-receiving part 16, extracting only an ACcomponent, amplifying the AC component, and generating an AC signal. Theamplification circuit 162 removes the DC component at or below apredetermined wavelength using, e.g., a high-pass filter, and buffersthe AC component using, e.g., an operational amplifier. The lightreception signal contains a pulsating component and a body movementcomponent. The amplification circuit 162 and the control circuit 161 arecapable of feeding a power supply voltage, for operating thelight-receiving part 16 at, e.g., reverse bias, to the light-receivingpart 16. In an instance in which the light-emitting part 14 isintermittently driven, the power supply to the light-receiving part 16is also intermittently fed, and the AC component is also intermittentlyamplified. The amplification circuit 162 is formed on, e.g., the motherboard (not shown), and wiring between the amplification circuit 162 andthe light-receiving part 16 is formed on, e.g., the substrate 11. Theamplification circuit 162 may also have an amplifier for amplifying thelight reception signal at a stage prior to the high-pass filter. In aninstance in which the amplification circuit 162 has an amplifier, theamplifier can be formed, e.g., on an end part of the substrate 11.

The A/D conversion circuit 163 converts an AC signal generated in theamplification circuit 162 into a digital signal (i.e., a first digitalsignal). The acceleration detecting part 166 detects, e.g.,gravitational acceleration in three axes (i.e., x-axis, y-axis, andz-axis) and generates an acceleration signal. Movement of the body(i.e., the arm), and therefore the movement of the biologicalinformation measuring device, is reflected in the acceleration signal.The A/D conversion circuit 167 converts the acceleration signalgenerated in the acceleration detecting part 166 into a digital signal(i.e., a second digital signal).

The digital signal processing circuit 168 uses the second digital signalto remove or reduce the body movement component in the first digitalsignal. The digital signal processing circuit 168 may be formed by,e.g., an FIR filter or another adaptive filter. The digital signalprocessing circuit 168 inputs the first digital signal and the seconddigital signal into the adaptive filter and generates a filter outputsignal in which noise has been removed or reduced.

The pulse rate computation circuit 164 uses, e.g., fast Fouriertransform (or in a broader sense, discrete Fourier transform) to performa frequency analysis on the filter output signal. The pulse ratecomputation circuit 164 identifies a frequency that represents apulsating component based on a result of the frequency analysis, andcomputationally obtains a pulse rate.

Using the wrist pulse rate monitor shown in FIG. 22 makes it possible toobtain, e.g., a time-series pulse rate information while the userperforms jogging or another exercise. The obtained pulse rateinformation can be used in a versatile manner such as for improving theconstitution of the user. However, situations such as the position ofthe wrist pulse rate monitor becoming displaced as a result of theexercise performed by the user, or the wrist pulse rate monitor beingaffected by external light, can be expected, and the number of factorsthat can reduce the detection accuracy (i.e., the measurement accuracy)is increased. Therefore, in order to secure a measurement that is ashigh as possible, it is preferable to take sufficient measures againstthe decrease in S/N due to light reflected near the surface of thecontact member (i.e., light-transmitting member). In this respect,sufficient measures against directly reflected light (i.e., invalidlight) have been implemented in the biological information detector 200as described above. It is thereby possible to obtain a novel wrist pulserate monitor that is capable of performing measurements with a highdegree of accuracy.

Fourth Embodiment

In the present embodiment, a description will be given for a pulseoximeter as another example of the biological information measuringdevice 300. A biological information detector (i.e., an in-vivo probe)installed in the pulse oximeter can be obtained using a configurationthat is identical to that in the previous embodiments (e.g., theconfiguration shown in FIGS. 1A and 2).

A description will be given based on the configuration shown in FIG. 1.The biological information detector 200 in the pulse oximeter includesthe light-emitting part 14 and the light-receiving part 16. Thelight-emitting part 14 emits, e.g., a red light and infrared light.Reflected light, produced by the light emitted by the light-emittingpart 14 reflecting at the detection site 1 (e.g., fingertip, arm, orwrist), is measured using the light-receiving part 16. Red-light andinfrared absorbance of haemoglobin in the blood differ depending onpresence of a bond with oxygen. Therefore, the arterial oxygensaturation (S_(p)O₂) can be measured by measuring the reflected light atthe light-receiving part 16 and analyzing the reflected light.

Components that have been reflected by an artery or the like andcomponents that have been reflected by a vein or soft tissue, which areincluded in all reflected light, can be distinguished from each otherusing the fact that pulsating components originate from arterial blood.It is also possible to count the pulse rate at the same time frompulsating pulse components.

The configuration of the biological information measuring part 202 foruse in a pulse rate monitor shown in FIG. 23 can be used as aconfiguration of the biological information measuring part for use inthe pulse oximeter. However, the pulse rate computation circuit 164shown in FIG. 23 is replaced by an arterial oxygen saturation analysiscircuit 164 in which a pulse rate computation circuit and an FFT oranother approach is used.

According to one aspect of a biological information detector of theEmbodiment, the biological information detector includes:

a light-emitting part;

a light-receiving part for receiving light having biologicalinformation, the light being emitted by the light-emitting part andreflected at a detection site of a test subject;

a reflecting part for reflecting the light having biologicalinformation;

a protecting part for protecting the light-emitting part, the protectingpart having a contact member provided with a contact surface in contactwith the detection site, the contact member being formed from a materialthat is transparent with respect to a wavelength of the light emitted bythe light-emitting part; and

a substrate arranged between the reflecting part and the protectingpart, the light-emitting part being arranged on a first surface towardsthe protecting part, the light-receiving part being arranged on a secondsurface, opposite the first surface towards the reflecting part, and thesubstrate being formed from a material that is transparent with respectto the wavelength of the light emitted by the light-emitting part;wherein

a once-reflected light, which is the light emitted from thelight-emitting part being reflected once on a contact-surface side ofthe contact member, is inhibited from being incident on thelight-receiving part.

According to the aspect described above, a component of the lightemitted by the light-emitting part that is the once-reflected light(i.e., directly reflected light), which has reflected once on thecontact-surface side of the contact member of the protecting part (i.e.,the contact surface and a vicinity of the contact surface (including aninterface between the contact surface and the detection site, as well asthe skin surface and an inner side of the skin) of the contact member,which is a light-transmitting member) is inhibited from being incidenton the light-receiving part.

Since the once-reflected light (i.e., directly reflected light; invalidlight) is inhibited from being incident on the light-receiving part, itis possible to minimize a decrease in the S/N of a detection signaloutputted from the light-receiving part.

According to another aspect of the biological information detector ofthe Embodiment, a twice-reflected light, which is the light emitted fromthe light-emitting part reflected twice on the contact-surface side ofthe contact member, is inhibited from being incident on thelight-receiving part.

According to the aspect described above, a component of the lightemitted by the light-emitting part that is the twice-reflected lightproduced by a double reflection on the contact-surface side of thecontact member of the protecting part (i.e., the contact surface and avicinity of the contact surface of the contact member, which is alight-transmitting member) is inhibited from being incident on thelight-receiving part.

Since the twice-reflected light (i.e., directly reflected light; invalidlight) is inhibited from being incident on a light-receiving region ofthe light-receiving part, it is possible to minimize a decrease in theS/N of the detection signal outputted from the light-receiving part.

According to another aspect of the biological information detector ofthe Embodiment, the reflecting part has a reflecting surface including apart of a spherical surface; the diameter of an outer circumferentialcircle of the reflecting part with respect to a plan view is set at apredetermined value; and in an instance in which there exist, as rangesof a focal distance of the reflecting part, a first focal distancerange, in which a ratio of a once-reflected incident light, which is theonce-reflected light reflecting on the reflecting surface and beingincident on the light-receiving part, with respect to a total amount ofreceived light is higher than a first threshold value; a second focaldistance range; and a third focal distance range, in which a ratio of atwice-reflected incident light, which is the twice-reflected lightreflecting on the reflecting surface and being incident on thelight-receiving part, with respect to the total amount of received lightis higher than a second threshold value; the focal distance of thereflecting surface is set within the second focal distance range, whichis between the first focal distance range and the third focal distancerange.

The reflecting part has a reflecting surface, and the reflecting surfaceincludes a part of a spherical surface, which is a quadric surface. Thereflecting surface has an outer circumferential shape that is circularwith respect to a plan view, and the diameter (i.e., the aperturediameter of the reflecting surface) of the circle (i.e., the outercircumferential circle of the reflecting surface) is set to apredetermined value.

According to the present aspect, changing the focal distance of thereflecting surface so as to, e.g., gradually increase results first in afocal distance range in which a ratio of light that is theonce-reflected light, which has reflected once on a contact-surface sideof the contact member, reflecting again at the reflecting surface andbeing incident on the light-receiving part (i.e., the once-reflectedincident light), with respect to a total amount of light received at thelight-receiving part, is higher than a predetermined threshold value(i.e., the first threshold value). This focal distance range is definedas the first focal distance range.

Further increasing the focal distance of the reflecting surface resultsnext in a focal distance range in which almost no directly reflectedlight (i.e., once-reflected light and twice-reflected light) reaches thelight-receiving part. This focal distance range is defined as the secondfocal distance range.

Further increasing the focal distance of the reflecting surface resultsin a focal distance range in which a ratio of light that is thetwice-reflected light, which has reflected twice on the contact-surfaceside of the contact member, reflecting again at the reflecting surfaceand being incident on the light-receiving part (i.e., thetwice-reflected incident light), in relation to the total amount oflight received at the light-receiving part, is higher than apredetermined threshold value (i.e., the second threshold value). Thisfocal distance range is defined as the third focal distance range. Thefirst threshold value and the second threshold value may be identical ormay differ from each other.

Based on the above observation, according to the aspect described above,the focal distance of the reflecting surface of the reflecting part isset within the second focal distance range, which is between the firstfocal distance range and the third focal distance range. Once the focaldistance of the reflecting surface is established, the curvature radiusof the spherical surface forming the reflecting surface is established(the curvature radius is twice the length of the focal distance). Thespherical surface is thereby unambiguously established. The aperturediameter of the reflecting surface is already known. This means that aposition at which the spherical surface is sliced along, e.g., an x-yplane is unambiguously established. A three-dimensional shape (andheight) of a reflecting surface including a part of the sphericalsurface is thereby established.

According to the aspect described above, the once-reflected light (i.e.,directly reflected light; invalid light) and the twice-reflected light(i.e., directly reflected light; invalid light) are inhibited from beingincident on the light-receiving part. It is thereby possible to reducethe effect of light reflected on the contact-surface side of the contactmember (e.g., a decrease in the S/N of the detection signal outputtedfrom the light-receiving part).

According to another aspect of the biological information detector ofthe Embodiment, the following relationship is true, given that φrepresents the diameter of the outer circumferential circle of thereflecting part; r represents the curvature radius of the sphericalsurface forming the reflecting surface; h represents the height of thereflecting surface, the height h being established in correspondencewith the curvature radius r and the diameter φ of the outercircumferential circle of the reflecting part and representing adistance between the second surface and a point of intersection betweenan optical axis and the reflecting surface; and Δh represents adifference between the height h of the reflecting surface and thecurvature radius r of the reflecting surface.

Mathematical formula 4r=√{square root over ({Δh ²+(φ/2)²})}  (4)

The aspect described above defines the curvature radius r of thespherical surface forming the reflecting surface. Specifically, giventhat φ represents the aperture diameter of the reflecting surface, hrepresents the height of the reflecting surface established incorrespondence with the aperture diameter φ and the curvature radius rof the spherical surface forming the reflecting surface, and Δhrepresents the difference between the height h of the reflecting surfaceand the curvature radius r of the reflecting surface, the curvatureradius r is represented by the above Equation (4).

In an instance in which the aperture diameter φ of the reflectingsurface is already known, when, for example, the focal distance df ofthe reflecting part is changed, the curvature radius r of the sphericalsurface forming the reflecting surface changes. When the curvatureradius r changes, the difference Δh between the height h and thecurvature radius r of the reflecting surface changes. The difference Δhand the focal distance df of the spherical surface forming thereflecting surface have a one-to-one correspondence relationship; whenthe focal distance df increases, the difference Δh also increases. Whenthe focal distance df of the reflecting part is established, thedifference Δh is established, and due to the Pythagorean theorem, theabove Equation 4 is established. Therefore, when a preferred focaldistance of the reflecting surface is established, it is possible to usethe above Equation 4 to unambiguously establish the curvature radius rof the reflecting surface, whereby the spherical surface forming thereflecting surface is established. Since the aperture diameter of thereflecting surface is already known, the three-dimensional shape and theheight of the reflecting surface are unambiguously established.

According to the aspect described above, it is thereby possible toobtain a reflecting part having a reflecting surface designed so thatthe effect of light reflected on the contact-surface side of the contactmember (e.g., a decrease in the S/N of the detection signal outputtedfrom the light-receiving part) can be reduced (e.g., throughoptimization design).

According to another aspect of the biological information detector ofthe Embodiment,

the reflecting part has a reflecting surface including a part of aparaboloid;

the paraboloid is a paraboloid of revolution having a z-axis as an axisof revolution, when a z-axis, among a mutually perpendicular x-axis, ay-axis, and the z-axis, is an optical axis;

the following relationship:

Mathematical formula 5z=(½r)·(x ² +y ²)  (5)

is established with regards to the paraboloid of revolution when anorigin is defined as a point of intersection between the z-axis and theparaboloid of revolution and r is defined as the curvature radius of thespherical surface in contact with the origin;

the diameter of an outer circumferential circle of the reflecting partwith respect to the plan view is set to a predetermined value; and

in an instance in which there exist, as ranges of a focal distance ofthe reflecting part,

a first focal distance range, in which a ratio of a once-reflectedincident light, which is the once-reflected light reflecting on thereflecting surface and being incident on the light-receiving part, withrespect to a total amount of received light is higher than apredetermined threshold value (i.e., a first threshold value);

a second focal distance range; and

a third focal distance range, in which a ratio of a twice-reflectedincident light, which is the twice-reflected light reflecting on thereflecting surface and being incident on the light-receiving part, withrespect to the total amount of received light is higher than apredetermined threshold value (i.e., a second threshold value),

the focal distance of the reflecting surface is set within the secondfocal distance range, which is between the first focal distance rangeand the third focal distance range.

According to the aspect described above, a paraboloid is used as aquadric surface that forms the reflecting surface of the reflectingpart. A paraboloid of revolution can be used as the paraboloid. Theparaboloid of revolution is a quadric surface obtained by revolving aparabola, using the z-axis, which is an axis of symmetry, as an axis ofrevolution, where the z-axis among the mutually perpendicular x-, y-,and z-axes that define a 3-dimensional space is the optical axis (i.e.,a curved surface represented by a quadratic equation with three unknownsof x, y, and z). When the origin (i.e., a surface origin) is defined asthe point of intersection between the z-axis and the paraboloid ofrevolution and r is defined as the curvature radius of the sphericalsurface in contact with the origin, the paraboloid of revolution can berepresented by the above Equation 5.

In an instance in which the aperture diameter φ of the reflectingsurface is already known, the focal distance df of the reflectingsurface and the curvature radius r of the spherical surface in contactwith the origin of the paraboloid forming the reflecting surface, forexample, have a one-to-one correspondence relationship. Therefore, whena preferred focal distance df is established, the curvature radius r ofthe spherical surface in contact with the origin is established, and theshape of the paraboloid of revolution is unambiguously established bythe above Equation 5. Also, since the aperture diameter of thereflecting surface is already known, a position at which the paraboloidof revolution is sliced along an x-y plane is thereby established. Thethree-dimensional shape and height of the reflecting surface includingthe paraboloid are thereby unambiguously established.

In an instance in which a reflecting surface including a part of aparaboloid of revolution is used, as with the instance described abovein which a reflecting surface including a part of a spherical surface isused, when the focal distance df is gradually increased, first, thefirst focal distance range appears, then the second focal distance rangeappears, then the third focal distance range appears. In the aspectdescribed above, the focal distance of the reflecting surface providedto the reflecting part is set within the second focal distance range,which is between the first focal distance range and the third focaldistance range. As described above, when the focal distance of thereflecting surface is established, the three-dimensional shape andheight of the reflecting surface are unambiguously established.According to the aspect described above, the reflecting part having,e.g., the reflecting surface that is optimized can thereby be obtained.The aspect described above thereby makes it possible to obtain thereflecting part having the reflecting surface that is, e.g., optimizedand that makes it possible to reduce the effect of light reflected onthe contact-surface side of the contact member (e.g., a decrease in theS/N of the detection signal outputted from the light-receiving part).

According to one aspect of the biological information measuring deviceof the Embodiment, there is provided a biological information measuringdevice including the biological information detector according to any ofthe above-mentioned aspects, and a biological information measuring partfor measuring the biological information according to a detection signaloutputted from the light-receiving part.

The biological information detector according to any of the aboveaspects are designed so as to be capable of reducing the effect of lightreflected on the contact-surface side of the contact member (e.g., adecrease in the S/N of the detection signal outputted from thelight-receiving part). The biological information measuring deviceprovided with the biological information detector is thereby capable ofmeasuring biological information to a high degree of accuracy. Specificexamples of the biological information measuring device include a pulserate monitor, a sphygmograph, and a pulse oximeter for measuringarterial oxygen saturation (SpO2).

According to another aspect of the biological information measuringdevice of the Embodiment, there is provided a biological informationmeasuring device in which the biological information is a pulse rate. Inthe aspect described above, the biological information measuring deviceis a pulse rate monitor. The blood vessel that is a biologicalinformation source is located within subcutaneous tissue located at thedetection site (e.g., a finger, arm, or wrist). Light emitted from thelight-emitting part provided to the pulse rate monitor reaches a bloodvessel and is reflected; a portion of the light also being partiallyabsorbed at the blood vessel. Due to an effect of the pulse, the rate ofabsorption at the blood vessel varies, and the amount of light reflectedat the blood vessel (i.e., light reflected at the detection site) alsovaries in correspondence with the pulse. Therefore, the light reflectedat the blood vessel contains pulse rate information as biologicalinformation. The pulse rate can therefore be measured according to abiological information detection signal outputted from thelight-receiving part (including a pulsating component corresponding tothe pulse).

The biological information measuring device may have a wristband capableof attaching the biological information detector to, e.g., a wrist (oran arm) of the test subject, and, e.g., a wrist pulse rate monitor (or awrist sphygmograph) is thereby realized. Using a wrist pulse ratemonitor makes it possible to obtain, e.g., a time-series pulse rateinformation while the user performs jogging or another exercise. Theobtained pulse rate information can be used in a versatile manner suchas for improving the constitution of the user. However, situations suchas the position of the wrist pulse rate monitor becoming displaced as aresult of the exercise performed by the user, or the wrist pulse ratemonitor being affected by external light, can be expected, and thenumber of factors that can reduce the detection accuracy (i.e., themeasurement accuracy) is increased. Therefore, in order to secure ahighly accurate measurement, it is preferable to take sufficientmeasures against the decrease in S/N due to light reflected near thesurface of the contact member (i.e., light-transmitting member) toincrease the S/N as much as possible. In this respect, the biologicalinformation detector according to any of the above aspects is designedso as to be capable of reducing the effect of light reflected on thecontact-surface side of the contact member (e.g., a decrease in the S/Nof the detection signal outputted from the light-receiving part) asdescribed above; therefore, the pulse rate monitor according to theaspect described above is capable of detecting the pulse rate to a highdegree of accuracy and at a high sensitivity, and can be readily appliedto a wrist pulse rate monitor.

A method for designing a reflecting part of a biological informationdetector of another aspect of the Embodiment includes: the biologicalinformation detector having: a light-emitting part; a light-receivingpart for receiving light having biological information, the light beingemitted by the light-emitting part and reflected at a detection site ofa test subject; a reflecting part having a reflecting surface forreflecting the light having biological information, the reflectingsurface including a part of a spherical surface or a part of aparaboloid, wherein the diameter of an outer circumferential circle ofthe reflecting surface with respect to the plan view is set to apredetermined value; a protecting part having a contact member providedwith a contact surface in contact with the detection site, the contactmember being formed from a material that is transparent with respect toa wavelength of the light emitted by the light-emitting part, andprotecting the light-emitting part; and a substrate arranged between thereflecting part and the protecting part, the light-emitting part beingarranged on a first surface towards the protecting part, thelight-receiving part being arranged on a second surface, opposite thefirst surface and towards the reflecting part, and the substrate beingformed from a material that is transparent with respect to thewavelength of the light emitted by the light-emitting part; determining,while changing the focal distance of the reflecting surface, a firstfocal distance range, in which a ratio of a once-reflected incidentlight with respect to a total amount of received light is higher than afirst threshold value. The once-reflected incident light being aonce-reflected light having reflected once on the contact-surface sideof the contact member reflecting on the reflecting surface and beingincident on a light-receiving region of the light-receiving part;determining, while changing the focal distance of the reflectingsurface, a third focal distance range, in which a ratio of atwice-reflected incident light with respect to a total amount ofreceived light is higher than a second threshold value, thetwice-reflected incident light being a twice-reflected light havingreflected twice on the contact-surface side of the contact memberreflecting on the reflecting surface and being incident on alight-receiving region of the light-receiving part; and setting thefocal distance of the reflecting surface in a second focal distancerange between the first focal distance range and the third focaldistance range.

The aspect described above shows a preferred method for designing thereflecting part of the biological information detector. The biologicalinformation detector has the reflecting part. The reflecting part hasthe reflecting surface, and the reflecting surface includes a part of aquadric surface. In the aspect described above, the reflecting surfaceincludes a part of a spherical surface or a part of a paraboloid. Theouter circumferential shape of the reflecting surface is circular withrespect to the plan view. For example, when the z-axis among themutually perpendicular x-, y-, and z-axes that define a 3-dimensionalspace is the optical axis, the outer circumferential shape of across-section surface formed by slicing the spherical surface along anx-y plane is circular, and the diameter of the circle (i.e., theaperture diameter of the reflecting surface) is set to a predeterminedvalue.

The behavior of the ratio of incident light corresponding to directlyreflected light that is reflected on the contact-surface side (i.e.,contact surface and a vicinity of the contact surface) of the contactmember (i.e., a light-transmitting member) and is incident on thelight-receiving part, with respect to the total amount of light receivedat the light-receiving part, is then examined while changing the focaldistance of the reflecting surface.

Changing the focal distance of the reflecting surface so as to, e.g.,gradually increase, results first in a focal distance range in which aratio of light that is the once-reflected light, which has reflectedonce on the contact-surface side of the contact member, reflecting againat the reflecting surface and being incident on the light-receiving part(i.e., the once-reflected incident light), with respect to a totalamount of light received at the light-receiving part, is higher than apredetermined threshold value (i.e., the first threshold value). Thisfocal distance range is defined as the first focal distance range.

Further increasing the focal distance of the reflecting surface resultsnext in a focal distance range in which almost no directly reflectedlight (i.e., once-reflected light and twice-reflected light) reaches thelight-receiving part. This focal distance range is defined as the secondfocal distance range.

Further increasing the focal distance of the reflecting surface resultsin a focal distance range in which a ratio of light that is thetwice-reflected light, which has reflected twice on the contact-surfaceside of the contact member, reflecting again at the reflecting surfaceand being incident on the light-receiving part (i.e., thetwice-reflected incident light), in relation to the total amount oflight received at the light-receiving part, is higher than apredetermined threshold value (i.e., the second threshold value). Thisfocal distance range is defined as the third focal distance range.

The focal distance of the reflecting surface of the reflecting part isset within the second focal distance range, which is between the firstfocal distance range and the third focal distance range. Once the focaldistance of the reflecting surface is established, the three-dimensionalshape and height of the reflecting surface are unambiguouslyestablished.

According to the aspect described above, it is possible to efficientlydesign a reflecting surface (i.e., a reflecting part) having preferablereflective characteristics, capable of minimizing incidence of theonce-reflected light (i.e., directly reflected light; invalid light) andthe twice-reflected light (i.e., directly reflected light; invalidlight) on the light-receiving part.

According to the embodiment described above, it is possible to reduce aneffect of directly reflected light when biological information is beingdetected.

A biological information detector according to the embodiment includes alight-emitting part, a reflecting part, a light-receiving part, aprotecting part, and a processing part. The reflecting part has a curveshaped reflecting surface that is configured to reflect light emitted bythe light-emitting part. The light-receiving part is configured toreceive incident light that is emitted by the light-emitting part andreflected at a detection site of a user. The protecting part isconfigured to protect the light-emitting part, and the protecting parthaw a contact surface adapted to contact with the detection site. Theprocessing part is configured to process a light reception signaloutputted from the light-receiving part. The light-emitting part has alight-emitting surface substantially in parallel to the contact surface,and a distance between the light-emitting surface and the contactsurface is within a range of 0.4 mm to 0.9 mm

According to the embodiment, the protecting part is formed from amaterial that is transparent with respect to a wavelength of the lightemitted by the light-emitting part.

According to the embodiment, the light emitted by the light-emittingpart is green in color and has a peak intensity within a wavelengthrange of 425 nm to 625 nm.

The biological information detector according to the embodiment furthercomprises a substrate supporting the light-emitting part, thelight-receiving part and the reflecting part, and the substrate is incontact with the protecting part. At least a part of the substrate iscoated with a transmitting material that transmits the light emitted bythe light-emitting part.

The biological information detector according to the embodiment furthercomprises an acceleration sensor configured to detect accelerationgenerated by the user and to output an acceleration signal to theprocessing part to remove or reduce a body movement component in thedigital signal outputted from the light-receiving part.

The biological information detector according to the embodiment furthercomprises a first A/D converter configured to convert the lightreception signal from the light-receiving part into a first digitalsignal, and a second A/D converter configured to convert theacceleration signal from the acceleration sensor into a second digitalsignal. The processing part generates the biological information usingthe first digital signal and the second digital signal.

Although a detailed description was given above concerning preferredembodiments of the inventions, persons skilled in the art should be ableto easily understand that various modifications can be made to theinvention. Accordingly, all of such examples of modifications are to beincluded in the scope of the invention. For example, terms stated atleast once together with different terms having broader sense oridentical sense in the specification or drawings may be replaced withthose different terms in any and all locations of the specification ordrawings.

What is claimed is:
 1. A biological information detector comprising: awristband adapted to be attached to a wrist of a user; a housingconnected to the wristband and adapted to be placed on the wrist of theuser; an opening defined in a surface of the housing adapted to face asurface of the wrist of the user; a light-emitting part disposed insidethe housing and configured to emit green light; a reflecting partdisposed in periphery of the light emitting part, and configured toreflect the light emitted by the light-emitting part, wherein thereflecting part is disposed inside the housing; a light-receiving partdisposed inside the housing, and configured to receive reflected lightreflected at a detection site of the wrist of the user; and a protectingpart configured to protect the light-emitting part and the reflectingpart, and is disposed at the opening of the housing to contact with thedetection site with the protecting part being disposed between thelight-emitting part and the detection site, the protecting part beingmade of a material that is transparent with respect to a wavelength ofthe light emitted by the light-emitting part, the protecting partincluding a first surface and a second surface, the first surface beingconfigured to contact the surface of the wrist of the user, the secondsurface being disposed between the first surface and the light-emittingpart, a thickness of a part of the protecting part that overlaps thelight-emitting part in a plan view being a uniform thickness, and thefirst surface and the second surface being flat surfaces.
 2. Thebiological information detector according to claim 1, wherein thereflecting part has a protruding part which protrude toward thedetection site and has a inclined surface which reflects the lightemitted by the light-emitting part.
 3. The biological informationdetector according to claim 1, wherein the light emitted by thelight-emitting part has a peak intensity within a wavelength range of425 nm to 625 nm.
 4. The biological information detector according toclaim 1, wherein the protecting part has a member which protrudes towardthe detection site from the housing.
 5. The biological informationdetector according to claim 1, further comprising: an accelerationsensor disposed inside the housing member, and configured to detect anacceleration signal generated from a motion of the user; a first A/Dconverter configured to convert the light reception signal from thelight-receiving part into a first digital signal; and a second A/Dconverter configured to convert the acceleration signal from theacceleration sensor into a second digital signal.
 6. The biologicalinformation detector according to claim 5, further comprising: aprocessing part disposed inside the housing, and configured to calculatea pulse rate using a light-reception signal outputted by thelight-receiving part.
 7. The biological information detector accordingto claim 6, wherein the processing part calculates the pulse rate usingthe first digital signal and the second digital signal.
 8. Thebiological information detector according to claim 1, wherein thelight-emitting part is configured to be driven intermittently.
 9. Thebiological information detector according to claim 1, wherein theprotecting part is spaced apart from the light-emitting part.